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| Home > Publications database > Two-zone model for the transport of wall released impurities in the edge plasma of a limiter tokamak |
| Home > Publications database > Two-zone model for the transport of wall released impurities in the edge plasma of a limiter tokamak |
| Book/Report | FZJ-2018-02731 |
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1987
Kernforschungsanlage Jülich, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/18386
Report No.: Juel-2115
Abstract: In two previous papers [1,2] some aspects of the impurity transport problem in the edge region of a tokamak plasma have been theoretically investigated under consideration of both parallel-field (toroidal) convection and cross-field (radial) convection and diffusion. It was shown that under certain restrictions concerning the thermalization between impurity and hydrogen ions an analytical solution of the drift-kinetic equation for the impurity ions can be constructed by a combination of the methods of characteristics and Laplace transforms, if the plasma background is assumed to be radially homogeneous. In order to simulate the strong radial variations, which the plasma parameters undergo in the edge region, a subdivision of the plasma background into several radially homogeneous zones discontinuously connected with each other has been devised. Within each plasma zone the impurity ion population is, of course, determined by both the transport processes as well as the volume and surface sources. The latter appear in the form of particle fluxes from the limiter and from or into the adjacent plasma zones. In order to obtain a uniform smooth solution of the impurity transport problem for the whole plasma region, the solutions for adjacent plasma zones have to be adjusted by requiring for each charge state continuity of both particle density and cross-field flux at the common boundary. If applied to the final solution, the matching procedure leads to an integral equation for either the particle density or the cross-field flux. One way of solving these integral equations is to incorporate the matching procedure directly in the Laplace transformed version of the drift-kinetic equation and to manage the additional complications in the inverse Laplace transformation. The success of this procedure depends on the choice of an appropriate variable for the Laplace transform, which should either be. common to all plasma zones or subject to a simple transformation when going from one plasma zone to another. Unfortunately, the convection time, which was used in the Laplace transform, in connection with the method of characteristics [1,2], does in general not fulfil the requirements of the above mentioned matching procedure [...]
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